(1) Field of the Invention
The present invention relates to light-sensitive compositions, particularly to light-sensitive compositions suitable for use in a presensitized plate from which a lithographic printing plate is to be prepared. More specifically, the invention relates to light-sensitive compositions suitable for use in preparation of presensitized plates having an excellent ink receptivity.
(2) Prior Art
Most light-sensitive substances actually used in presensitized printing materials are diazonium compounds, and the most commonly used conventional substances among the diazonium compounds are diazo resins (i.e., diazonium salt condensates) represented by formaldehyde condensates of p-diazodiphenylamine.
Compositions of the light-sensitive layer of presensitized plates using diazo resins can be classified into two types, i.e, one comprising a diazo resin alone, namely those not using a binder, as disclosed, for example, in U.S. Pat. No. 2,714,066, and another comprising a mixture of an diazo resin and a binder, as disclosed, for example, in U.S. Pat. No. 4,275,138. Recently, many presensitized plates using diazonium compounds have a light-sensitive layer comprising a diazonium compound and a binder so as to impart a high printing durability to the plates.
Known light-sensitive layers of this type include, as disclosed in U.S. Pat. No. 4,275,138, so-called alkali development type layers where unexposed areas are removed (developed) with an aqueous alkali developing solution, and so-called solvent development type layers where unexposed areas are removed with an organic solvent series developing solution. Recently, in view of safety and worker hygiene, alkali development type light-sensitive layers have received attention, and it is mainly the properties of the binder determines the type to which the light-sensitive layer belongs. Methods of making a binder having an alkali development property include a method as disclosed in the aforementioned U.S. Pat. No. 4,275,138 where monomers containing carboxylic acid groups are copolymerized, a method as disclosed in U.S. Pat. No. 2,861,058 where polyvinyl alcohol is reacted with a cyclic acid anhydride such as phthalic anhydride through hydroxyl groups of the former to introduce carboxylic acid groups in the polymer, etc. However, the resulting light-sensitive layers were inadequate in ink receptivity which is an important characteristic of a lithographic printing plate.
Thus, a method where a high molecular compound is added has been proposed for improvement of ink receptivity, as disclosed in U.S. Pat. No. 4,294,905, but this method is still inadequate, and further improvement has been desired.